The invention relates to electrophotographic apparatus having an improved developer station. More specifically, the invention relates to the manner in which the movement of developer material is controlled so that it is advanced in one direction incrementally each time it is cycled to developer and transport rollers, and moved in the opposite direction when it approaches one end of the developer station.
In electrophotographic copier/duplicators an electrostatic image of an original document is formed on a belt, drum or the like. The image is developed by applying toner particles thereto in a developer station. The toner particles are subsequently transferrred to a copy sheet and fused to the sheet to form a copy of the original document.
Major concerns in the design of a developer station are to minimize power requirements, provide adequate mixing and electrostatic charging of developer material, minimize changes in developer material properties due to aging, and to provide a stable and uniform flow of developer material. In developer station design, however, these concerns often conflict. For example, the desire for low power input may conflict with the need for good mixing of the developer material. This invention provides an arrangement of a partitioned storage hopper, one auger, and a magnetic transport roller, along with other components, to provide a desirable compromise among the major concerns referred to above.
Various types of apparatus have been devised for controlling the flow of developer material in a developer station. For example, U.S. Pat. Nos. 3,697,050 and 3,724,422 each disclose a cross-mixing baffle for controlling the mixing of developer material. The baffle has a plurality of chutes on one side which direct developer material in one lateral direction, and a plurality of similar chutes on the other side which direct developer material in the opposite direction. The number and size of the chutes are selected to equalize cross flow of the material in both directions. U.S. Pat. No. 3,707,947 also discloses cross-mixing apparatus wherein channels in one bank are slanted in one direction and channels in another bank are slanted in the opposite direction.
U.S. Pat. No. 3,943,887 teaches a hybrid cross-mixer comprising an auger-type "active" section and two "passive" sections. In the active section a right-hand helix and a left-hand helix mounted on the same shaft move developer from the central portion of the development zone outwardly toward the edges thereof. The two passive sections have baffles that deflect developer from the outer portions inwardly toward the center of the housing.
U.S. Pat. No. 3,947,107 illustrates an active crossmixer having a pair of rotatable augers that are driven in opposite directions to advance developer along a sump. The sump has apertures therethrough so that the developer not only flows over the end of the baffles but also through the baffle, thereby distributing the developer across the sump.
The developer station disclosed in U.S. Pat. No. 3,949,704 comprises a cross-mixing baffle across which developer flows on the way to a screen, then through the screen and to an impeller which moves the developer toward the magnetic brushes. Similar disclosures are found in U.S. Pat. Nos. 3,906,898; 3,865,081 and 3,872,830.
Several patents show passive cross-mixing apparatus in combination with magnetic gates for controlling the flow of developer into the sump. These patents include U.S. Pat. Nos. 3,908,596; 3,927,640 and 3,930,466.
Lateral mixing of toner across the developer area, primarily by the use of two screws driven in opposite directions is discussed in U.S. Pat. Nos. 2,910,964; 3,912,388; 3,145,122 and 3,246,629.
U.S. Pat. No. 3,572,289 discloses cross-mixing baffles of the snow-plow type. The patent states that these baffles eliminate the need for power driven cross-mixing augers within a sump.
Canadian Pat. No. 951,114 discloses obstacles in the shape of pins or plows located along the flow path for developer for deflecting the developer and thereby directing it from a narrow band into a wider band.